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) SAMPLE PAPER I
XII - PHYSICS
Time : Three Hours Max. Marks : 70
General Instructions
(a) All questions are compulsory.
(b) There are 30 questions in total. Questions 1 to 8 carry one mark each, questions 9 to 18 carry two marks each, questions 19 to 27 carry three marks each and questions 28 to 30 carry five marks each.
© There is no overall choice. However, an internal choice has been provided in one question of two marks, one question of three marks and all three questions of five marks each. You have to attempt only one of the given choices in such questions.
(d) Use of calculators is not permitted.
(e) You may use the following physical constants wherever necessary :
c = 3 x 108 ms-1
h = 6.6 x 10-34 Js
e = 1.6 x 10-19Co
μ=17AmT10x4−−π
Boltzmann constant k = 1.38 x 10-23 J/K
Avogadro’s number NA= 6.023 x 1023/mole
Mass of neutron mn= 1.6 x 10-23
1. Two identical charged particles moving with same speed enter a region of uniform magnetic field. If one of these enters normal to the field direction and the other enters along a direction at 300 with the field, what would be the ratio of their angular frequencies?
2. Why does a metallic piece become very hot when it is surrounded by a coil carrying high frequency alternating current?
3. How is a sample of an n-type semiconductor electrically neutral though it has an excess of negative charge carriers?
4. Name the characteristics of electromagnetic waves that
(i) increases
(ii) remains constant
in the electromagnetic spectrum as one moves from radiowave region towards ultraviolet region.
5. How would the angular separation of interference fringes in young’s double slit experiment change when the
distance of separation between the slits and the screen is doubled?
6. Calculate the ratio of energies of photons produced due to transition of electron of hydrogen atom from its,
(i) Second permitted energy level to the first level, and
(ii) Highest permitted energy level to the second permitted level
7. Give expression for the average value of the a c voltage
V = V0Si t ω
(4)over the time interval t = 0 and t = 8. How is the band gap, Eg, of a photo diode related to the maximum wavelength ,m , that can be detected by it?
9. Keeping the voltage of the charging source constant, what would be the percentage change in the energy stored in a parallel plate capacitor if the separation between its plates were to be decreased by 10%?
10. Explain how the average velocity of free electrons in a metal at constant temperature, in an electric field, remain constant even though the electrons are being constantly accelerated by this electric field?
A straight thick long wire of uniform cross section of radius ‘a’ is carrying a steady current I. Use Ampere’s circuital law to obtain a relation showing the variation of the magnetic field (Br) inside and outside the wire with distance r, () and () of the field point from the centre of its cross section. Plot a graph showing the nature of this variation. Calculate the ratio of magnetic field at a point above the surface of the wire to that at a point below it surface. What is the maximum value of the field of this wire? 5
29. State the principle which helps us to determine the shape of the wavefront at a later time from its given shape at any time. Apply this principle to
(i) Show that a spherical/ plane wavefront continues to propagate forward as a spherical/plane wave front.
(ii) Derive Snell’s law of refraction by drawing the refracted wavefront corresponding to a plane wavefront incident on the boundary separating a rarer medium from a denser medium.
OR
What do we understand by ‘polarization’ of a wave? How does this phenomenon help us to decide whether a given wave is transverse or longitudinal in nature?
Light from an ordinary source (say a sodium lamp) is passed through a polaroid sheet P1 .The transmitted light is then made to pass through a second polaroid sheet P2 which can be rotated so that the angle () between the two polaroid sheets varies from O0to 90o. Show graphically the variation of the intensity of light, transmitted by P1andP2, as a function o the angle . Take the incident beam intensity as I0. Why does the light from a clear blue portion of the sky, show a rise and fall of intensity when viewed through a polaroid which is rotated? 5
30. A student has to study the input and output characteristics of a n-p-n silicon transistor in the Common Emitter configuration. What kind of a circuit arrangement should she use for this purpose?
Draw the typical shape of input characteristics likely to be obtained by her. What do we understand by the cut off, active and saturation states of the transistor? In which of these states does the transistor not remain when being used as a switch?
OR
Input signals A and B are applied to the input terminals of the ‘dotted box’ set-up shown here. Let Y be the final output signal from the box. Draw the wave forms of the signals labelled as C1 and C 2 within the box, giving (in brief) the reasons for getting these wave forms. Hence draw the wave form of the final output signal Y. Give reasons for your choice.
What can we state (in words) as the relation between the final output signal Y and the input signals A and B ?
A straight thick long wire of uniform cross section of radius ‘a’ is carrying a steady current I. Use Ampere’s circuital law to obtain a relation showing the variation of the magnetic field (Br) inside and outside the wire with distance r, () and () of the field point from the centre of its cross section. Plot a graph showing the nature of this variation. Calculate the ratio of magnetic field at a point above the surface of the wire to that at a point below it surface. What is the maximum value of the field of this wire? 5
29. State the principle which helps us to determine the shape of the wavefront at a later time from its given shape at any time. Apply this principle to
(i) Show that a spherical/ plane wavefront continues to propagate forward as a spherical/plane wave front.
(ii) Derive Snell’s law of refraction by drawing the refracted wavefront corresponding to a plane wavefront incident on the boundary separating a rarer medium from a denser medium.
OR
What do we understand by ‘polarization’ of a wave? How does this phenomenon help us to decide whether a given wave is transverse or longitudinal in nature?
Light from an ordinary source (say a sodium lamp) is passed through a polaroid sheet P1 .The transmitted light is then made to pass through a second polaroid sheet P2 which can be rotated so that the angle () between the two polaroid sheets varies from O0to 90o. Show graphically the variation of the intensity of light, transmitted by P1andP2, as a function o the angle . Take the incident beam intensity as I0. Why does the light from a clear blue portion of the sky, show a rise and fall of intensity when viewed through a polaroid which is rotated? 5
30. A student has to study the input and output characteristics of a n-p-n silicon transistor in the Common Emitter configuration. What kind of a circuit arrangement should she use for this purpose?
Draw the typical shape of input characteristics likely to be obtained by her. What do we understand by the cut off, active and saturation states of the transistor? In which of these states does the transistor not remain when being used as a switch?
OR
Input signals A and B are applied to the input terminals of the ‘dotted box’ set-up shown here. Let Y be the final output signal from the box. Draw the wave forms of the signals labelled as C1 and C 2 within the box, giving (in brief) the reasons for getting these wave forms. Hence draw the wave form of the final output signal Y. Give reasons for your choice.
What can we state (in words) as the relation between the final output signal Y and the input signals A and B ?